Traditionally, hexotonal is produced by an addition of TNT, powdered aluminum and wax to a hexotol melt (hexogen+TNT). The thus obtained hexotonal mixture is thereafter cast to desired configuration. Thus, the direct manufacture of hexotonal has hitherto been effected in the explosives foundry in immediate association with its final shaping. This has entailed that part of the capacity of the explosives foundry has had to be devoted to other operations than the primary duty of the foundry, namely that of casting explosives into blasting charges or other explosive devices of the desired type. Furthermore, the handling of, above all the powdered aluminum is fraught with considerable risks, since this powder, on the one hand, reacts with water on being heated, generating hydrogen gas, and, on the other hand, the powdered aluminum shows a marked tendency to initiate dust explosions.
Octonal is traditionally manufactured in a corresponding manner and, as a result, that which generally applies in the manufacture of hexotonal also applies in principle to the manufacture of octonal.
Users within this Art have long voiced the wish to have access to a granulate hexotonal and octonal, respectively, which may be directly melted down and cast to the desired form. It would, namely, thereby become possible to transfer a perilously delicate manufacturing stage to the explosive makers and, at the same time, make available further resources in the user's own explosive foundry. For safety reasons, granules containing crystalline explosive substances such as hexogen and octogen are primarily manufactured by so-called wet granulation. This method has long been known in the Art, and a method particularly well-suited for granulation of TNT-containing composite explosives which also contain crystalline components is described in Swedish Pat. No. 158.663.
However, granulate hexotonal and octonal cannot be produced by wet granulation without further ado, since, as has previously been pointed out, hydrogen gas is, as a rule, generated on heating of powdered aluminum in water. It speaks for itself that an uncontrollable hydrogen gas generation in conjunction with the handling of a substance which is explosive, per se, cannot, for reasons of safety, be accepted. While, for example, an aluminum sheet surface in its pure form is protected by a natural oxide layer of Al.sub.2 O.sub.3, this layer is hydroscopic and dissolves spontaneously in both acidic and basic solutions. Furthermore, powdered aluminum has a large specific surface area with many sharp corners, for which reason it reacts with hot water under violent hydrogen gas generation. Apart from wet granulation, a protected aluminum powder may also give rise to a certain hydrogen gas generation if a finished, aluminous explosive is stored in a damp and warm environment.
With a view to obviating the problems inherent in hydrogen gas generation in association with water, attempts have been made in this Art to inactivate the powdered aluminum by treating it with isostearic acid and/or stearic acid. However, this treatment method entails that the powdered aluminum shows a strong tendency to flocculate with the wax which is generally employed as phlegmatization agent in wet granulation of TNT with pararefractory crystalline or granulate substances such as hexogen or octogen, respectively. In its turn, this flocculation tendency impedes the production of homogeneously cast hexotonal and octonal, respectively, from powdered aluminum treated in this manner. This problem is aggravated by the fact that hexotonal and octonal are in themselves more sensitive to mechanical stresses than hexotol and octol and, consequently, generally contain more phlegmatization wax.
It has now, however, become possible, in accordance with the present invention, to produce granulated hexotonal and octonal, respectively, by wet granulation without the risk of an uncontrollable hydrogen gas generation on granulation or storage of the finished product and without, at the same time, imparting to the powdered aluminum such a propensity for flocculation that the finished product becomes inhomogeneous. The granulated hexotonal and octonal, respectively, produced according to the present invention may either be employed directly as low density charges or, after melting, be cast to high density charges.
The previously-mentioned Swedish Pat. No. 158.663 discloses a method of wet granulation of TNT-containing composite explosives, such as hexotol and octol, according to which an aqueous suspension is produced in a first stage (the primary stage) of all of the components included in the finished explosive apart from the TNT, there being then added, at a temperature which exceeds the melting point of the TNT, an amount of the TNT (=primary TNT) which has been empirically established as giving a homogeneous and non-tacky granulate together with the other components, when the mixture is cooled to below the melting point of the TNT. The thus obtained primary granules are subsequently placed in their mother liquor or in another suspension agent at a temperature below the melting point of the TNT, together with the molten remaining amount of TNT (=the secondary TNT). The secondary TNT then forms a coating on the primary granules. If the added amount of primary TNT is insufficient, inhomogeneous granules will readily be formed, and if this amount is excessive, there is the risk that the TNT be deposited, on cooling, in the form of a solid cake instead of forming granules with the other components.
Another aspect of the state of the Art is described in the 1976 NTIS report AD-A074705, by J. F. Drolet and R. R. Lavertn, relating to "Development of a Method to produce high Energy Blasting Prills". This report describes a method for producing pellets of TNT-aluminum-containing explosives which may also contain hexogen or octogen. The method is based on the concept that droplets of a melt containing the contemplated components are allowed to harden while falling through a water-filled cooling tower. In order to avoid a reaction between the powdered aluminum and the water, the former is deactivated by a minor addition of ammonium lignosulphonate.
A further aspect of the state of the Art consists of Norwegian Pat. No. 144666 (EPO Application No. 0035 376) which describes a method for the preparation of hexotonal and octonal, respectively, by wet granulation in water of hexogen (or octogen, respectively), wax and powdered aluminum treated so as to withstand water, to a first component A which is mixed and melted together with a second component B, consisting of TNT and possibly cellulose dinitrate and lecithin. The method as such is somewhat circumstantial and, for safety reasons, can only be put into effect employing powdered aluminum which is treated so as to withstand water.